1. Field of the Invention
The present invention relates generally to electromagnetic field measuring devices and more particularly to an optically powered amplifier which amplifies an electrical signal from antenna and then provides the amplified signal to an electro-optic modulator.
2. Description of the Prior Art
The detection and measurement of hazardous electromagnetic radiation which poses a biological threat to humans and animals has become increasingly more important with the rapid proliferation of electronic devices such as micro-wave ovens, marine radar systems, medical apparatus and the like. It is even believed that transmission lines and other high voltage power distribution devices can cause biological damage to humans routinely exposed to intense electric fields for extended periods of time. There is thus a need for an instrument for measuring electric field intensity which is portable, easy to operate and reliable.
In the past electromagnetic field sensing apparatus have made use of a metallic antenna coupled by an electrically conductive transmission line, such as a coaxial cable, to a receiver unit to measure incident electromagnetic fields. There are several disadvantages to this type of electromagnetic field sensing including the perturbation of the electromagnetic field being measured by the metallic antenna and the transmission line and limited transmission line length (approximately ten meters for microwave frequency signals).
A second type of electromagnetic field sensing apparatus make use of the properties of electro-optic crystals to measure the intensity of an incoming electromagnetic field. For example, U.S. Pat. No. 4,070,621 to Bassen et. al. discloses a wideband, passive detector of electromagnetic fields which includes a dipole antenna electrically coupled to an electro-optic modulator with the dipole antenna converting electromagnetic fields incident on the antenna to a voltage signal which is supplied to the modulator. A light source transmits light through the modulator with the modulator modulating the light passing through the modulator. A detector then receives the modulated light and measures, for example, the amplitude, phase and frequency of the incoming electromagnetic fields. However, these electromagnetic field sensing apparatus, such as Bassen's wideband, passive detector do not have the sensitivity to measure low level electromagnetic fields.
With these and other disadvantages known to the prior art electromagnetic field sensing apparatus the present invention was conceived and one of its objects is to provide an electromagnetic field sensing apparatus for monitoring electromagnetic radiation in free space or in the near field of a radiation source in an improved manner.
It is another object of the present invention to provide a relatively simple in design, yet highly reliable electromagnetic field sensing apparatus.
It is yet another object of the invention to provide a portable electromagnetic field sensing apparatus.
Various other advantages and objects of the present invention will become apparent to those skilled in the art as a more detailed description of the invention is set forth below.